Radio receiver



0% 29, 1936. w. 1.. CARL'SON RADIO RECEIVER Filed Aug. 15, 1935 Rn wfifi u r a mc L l l e d m -m w -kn-fim LQBQR mw Till Q EN 2 .2 m 2 a \H\HN Patented Dec. 29, 1936 UNETED STATES PATENT OFFIQE.

RADIO RECEIVER of Delaware Application August 15, 1933, Serial No.685,196

16 Claims.

My invention relates to radio receivers and particularly to receivers ofthe superheterodyne type designed to receive signals over a plurality offrequency ranges.

Various circuits have been utilized for adapting radio receivers,designed primarily for reception within the broadcast band, to receivesignals within a different frequency band. One such circuit is generallyknown as a short-wave converter and consists of an oscillator and tunedradio-frequency circuit which may be connected to a conventionalbroadcast receiver at the proper point in the circuit whereby the highfrequency or short-wave signals are converted to the intermediatefrequency signals for which the broadcast receiver is designed.

The converter type of circuit is satisfactory in operation, but it isobjectionable in that it is both expensive and lacking in compactnessbecause of the additional apparatus required.

A circuit of another type involves switching different sets of coilsinto the radiofrequency and oscillator circuits for the differentfrequency ranges. This is objectionable in many cases both because ofthe switching and of the added space required for the extra coils andbecause of the added cost.

One of the main objects of my invention is to provide a simplifiedreceiver suitable for operation over a plurality of frequency bandswhich may be made relatively low in cost and compact in construction.

A further object of my invention is to provide a superheterodyne type ofreceiver which does not require a change in the oscillator adjustmentwhen switching from one frequency range to another, whereby thelining-up of the oscillator and the tuned radio-frequency circuits isfacilitated.

In practicing one embodiment of my invention I design the receiver toreceive signals within a band lying between 540 kilocycles and 1710kilocycies, which will be referred to as the broadcast band, and withina narrow high frequency band lying between 2400 kilocycles and 2500kilocycles, which will be referred to as the police band.

Reception within the high frequency band, within which police calls maybe heard, is accomplished by utilizing the second harmonic of the outputof the superheterodyne oscillator and by tuning the radio frequencycircuit broadly to a rind-point in the high frequency band.

The radio frequency circuit is tuned to the high frequency band byconnecting a small condenser in series with the tuning condenser,whereby a change in setting of the tuning condenser will have verylittle effect upon the capacity shunted across the inductance coil ofthe radio frequency circuit and, consequently, very little effect uponthe tuning of that circuit. During reception within the broadcast band,the small condenser is short-circuited so that the tuning condenser iseffective for tuning the radio frequency circuits in the usual way.

Other features and'advantages of my invention will appear from thefollowing description taken in connection with the accompanying drawingin which:

Figure 1 is a circuit diagram of a radio receiver embodying myinvention; and

Fig. 2 is a circuit diagram of one of the circuits of the receiver ofFig. 1, illustrating a modified form of my invention.

Referring to Fig. 1, the preferred embodiment comprises a tuned radiofrequency amplifier which includes a suitable amplifier device such asan electronic tube 1 having, in the present example, an indirectlyheated cathode 3, a control grid 5, a screen grid 1, a suppressor grid9, and an anode H. The tuned input or signal selecting circuit of thevacuum tube I, designated by the reference numeral l3, includes a radiofrequency transformer l5 having a primary winding I! and a secondarywinding IS. The primary winding I1 is connected with a signal collectingmeans such as an antenna 2 I and a ground as indicated.

The secondary winding [9 is shunted by a variable tuning condenser 23and a small adjustable condenser 25 connected in series therewith, thecondenser 25 being provided for the purpose of tuning the input circuitl3 to a frequency in the middle of the high frequency or police band.

A switch 21 is provided in conjunction with the condenser 25 to permitit to be made ineffective and whereby the tuning condenser 23 may beconnected directly across the secondary winding IQ for tuning over thebroadcast band. In the present example and as a preferred arrangement,the switch 21 is arranged to short circuit the condenser 25.

The control grid 5 of the amplifier device or tube l is connected to apoint tapped down on the secondary winding I9 in order to reduce theeffect of the tube input capacity on the tuned circuit I 3. While thisreduces the gain of the circuit somewhat, it permits making the receivertunable in the broadcast band over the desired frequency range.

The output circuit of the amplifier tube I is coupled to the tuned inputcircuit 29 of the combined first detector and oscillator tube 3|. Theoutput circuit of the vacuum tube I may be traced from the anode I Ithrough the primary winding 33 of a radio frequency transformer 35, andthrough conductors 31 and 39 to a point of positive potential on avoltage divider means 4| which is connected with a power supply means43. A radio frequency connection from the low potential end of primarywinding 33 to the oathode 3 is provided through a bypass condenser 44and a bypass condenser 46 shunting a portion of voltage divider 4|.

The tuned input or selecting circuit 29 of the first detector is similarto the tuned radio frequency circuit I3 above-described, and-includesthe secondary winding 45 of the radio frequency transformer 35 which isshunted by a variable condenser 47 and a small adjustable condenser 49connected in series therewith.

A switch 5| is connected across the condenser 49, this switch beingoperated simultaneously with and for the same purpose as the switch 21by means of a common control as indicated by the dotted line connection53.

The tuning condensers 23 and 41 are units of a gang condenser and areoperated simultaneously by means of a common control as indicated by thedotted line connection 55. They are shunted by small trimmer condensers51 and 59, respectively, for lining-up the tuned circuits over thebroadcast band in the usual way.

The control grid 6| of the first detector is connected to a point tappeddown on the secondary winding 45 in order to obtain the desired tuningrange as explained above.

The connections of the low potential ends of the tuned circuits I3 and29 to the cathodes 3 and 63 may be traced through conductors '65 and 61,respectively, to the common conductor 69, and through a grid biasingportion 'II of the voltage divider 4| and a conductor I3 to the cathode3, this cathode being connected to the cathode 63 of the tube 3| througha conductor 15.

, It will be noted that the radio frequency connection from the tunedcircuits I3 and 29 to the cathodes is through the bypass condenser 46shunting the biasing resistor portion 'II.

The detector electrodes, which are enclosed in the same envelope withthe oscillator electrodes,

comprise the cathode 63 and control grid 6|, above referred to, a screengrid I9 and an anode 8|. The screen grid 19 and the screen grid 1 of theradio frequency amplifier tube I are connected through conductors 83 and85, respectively, and through a conductor 81 to a point of positivepotential on the voltage divider 4|. lhe screen grids have a radiofrequency connection to ground through a condenser 86 and a condenser 88as indicated.

The detector anode BI is connected to the primary winding 89 of a tunedintermediate frequency transformer 9|, and receives an operatingpotential through a resistor 93 and a conductor 95 from a positive pointon the voltage divider 4|, as indicated.

The oscillator electrodes comprise a control grid 91, an anode electrode99 and the cathode 63 which is common to the detector and oscillator. Byutilizing a common cathode 63, the detector and oscillator are coupledthrough the common electron stream. It is to be understood that anysuitable oscillator and coupling circuit may be employed in practicingmy invention, but

the oscillator shown in Fig. l is especially satisfactory as it is richin second harmonic.

The frequency determining circuit I66 of the oscillator includes aninductance coil I 6| which is shunted by a variable condenser I63 and afixed condenser I65 connected in series, the fixed condenser I65 havinga larger capacity than the minimum capacity of the variable condenserI63. The variable condenser I63 is one unit of the above-mentioned gangcondenser and is tuned simultaneously with the condensers 23 and 41 bymeans of the common tuning control indicated by the dotted lineconnection 55.

The fixed condenser I65 is employed in series with the variablecondenser I63 for the purpose of making the oscillator track with thetuned radio frequency circuits as described in Carlson Patent No.1,740,331, and forms no part of my present invention.

The oscillator variable condenser I63 is shunted by a small trimmercondenser I6! for the purpose of lining-up the oscillator with the tunedcircuits I9 and 29.

The high potential end of the inductance coil I6I is coupled to theoscillator control grid 91 through a coupling condenser I69 and a gridleak coupling resistor |I3 to cathode, while the point between the fixedcondenser I65 and the variable condenser I63 is provided with a radiofrequency path to the cathode 63 through a circuit which may be tracedthrough the conductors I II and 69, the bypass condenser 46 and theconductors I3 and I5 to the cathode 63.

The plate circuit of the oscillator is coupled to the tuned oscillatorcircuit I66 for producing sustained oscillations by means of aninductance or feedback coil H5. The plate circuit of the oscillator maybe traced from the plate electrode 99 through the feedback coil I I 5and through the resistor 93 and the conductor 95 to the voltage dividerM. A radio frequency bypass condenser II! is connected between the upperend of the resistor 93 and the conductor I I I.

It will be apparent that when the switches 27 and 5| are closed, thereceiver functions as a conventional superheterodyne receiver, theoscillator beating with the incoming signal to produce an intermediatefrequency signal output in the detector plate circuit which istransferred through the tuned transformer 9| to the second detectorindicated at II 9. In the embodiment being described, an intermediatefrequency of kilocycles is employed.

When the switches 21 and 5| are open, the radio frequency tuningcondensers 23 and 41 are made substantially ineffective since they areconnected in series with condensers having, rela tively, very smallcapacities. In one embodiment of my invention, the low capacitycondensers 25 and 49 have capacity values ranging between 3micro-microfarads and 16 micro-microfarads, while the tuning condensers23 and 41 each have capacity values ranging between 18 micro-microfaradsand 405 micro-microfarads. Since the condensers 25 and 49 will generallybe set in the middle region of their range, at 9 micro-microfarads, forexample, it is evident that the capacity of the series combination ofcondensers is not varied appreciably by varying the capacity of thelarge condenser, even when the large condenser is set near its minimumcapacity value.

The secondary windings I9 and 45 are given considerable distributedcapacity so that they have a natural resonant period in the neighborhoodof the police band. In order that the selecting' circuits may always .betuned to themiddle of the high frequency or police band, the distributedcapacity of .each secondary winding is made such that together with thetube input capacity, the secondary windings are normally tuned to afrequency slightly above said high frequency band. i

The assembled apparatus is then adjusted with the switches 21 and 5|open, the small condensers Z5 and 49 being adjusted to a value such thatthe circuits I3 and 29 are. tuned to-the middle of the high frequency orpolice band. In the particular embodiment being described, thecondensers 25 and 49 are adjusted to tune the circuits I3 and 29,respectively, to a frequency of z i lokilocycles.

As previously stated, the tuning at the police band is so broad thatsignals at all frequencies lying between 2400 kilocycles and 2500kilocycles are passed by the tuned circuits I 3 and 29. Within thisbandthe desired station is selected solely by adjusting the oscillatorfrequency to a value such that the difference between the secondharmonic of the oscillator signal output and the frequency of theincoming signal is 175 kilocycles. From the foregoing description of thetuned circuits I3 and 29, it will be understood that although thecondensers 23 and 4'! are rotated at the same time the oscillatorfrequency is adjusted, there is substantially no change in the tuning ofthese circuits.

The oscillator may be designed to supply a fundamental frequencyoscillation which is either 175 kilocycles above or below the frequencyto which the selecting circuits are tuned in the broadcast band. In thepreferred embodiment the oscillator is adjusted to supply the higherfrequency oscillations, but it will be seen that, in either case, thesecond harmonic falls within the range required for reception within thepolice band.

It will be apparent that, within the police band, a station can bereceived at either one or two oscillator settings, but that two stationswill never be received at one oscillator setting since the frequencyresponse range of the fixedly tuned selecting circuit is less than theintermediate frequency.

In Fig. 2 there is illustrated a tuned radio frequency or selectingcircuit which may be substituted for the circuits I3 and 29 shown inFig. 1.

Referring to Fig. 2, where parts similar to those in Fig. 1 areindicated by like reference numerals, the secondary I9 of the radiofrequency coupling transformer I5 is provided with the variablecondenser 23 for tuning over the broadcast band and with a smalladjustable condenser I 2| for tuning over the higher frequency or policeband.

An inspection of Figs. 1 and 2 will show that a feature common to thetwo circuits is that of having fixed tuning for the police band whilepermitting the broadcast tuning condensers to be varied during theadjustment of the oscillator frequency. In both circuits, the stationsin the police band are selected by causing the oscillator to producearsecond harmonic frequency of the proper value.

By employing my invention, a small receiver of the so-called midget typemay be made tunable over a plurality-of frequency ranges without addingmaterially to its production cost. Specifically, my invention permits alow production cost because only a few small parts need to be added tothe usual single range receiver and also because it permits lining-upthe tuned radio frequency circuits and the oscillator in the usual way.The last feature is of special importance because any design which makesa lineup for uni-control difficult necessarily adds to the cost ofassembly.

Various other modifications may be made in my invention withoutdeparting from the spirit and scope thereof, and I desire, therefore,that only such limitations shall be placed thereon as are necessitatedby the prior art and set forth in the appended claims.

I claim as my invention:

1. In a receiver of the superheterodyne type, a detector, an oscillatorincluding means for producing oscillations having a selected frequencyand a harmonic frequency thereof, said oscillator being coupled to saiddetector, a selecting circuit coupled to said detector, said circuitcomprising an inductance coil, a variable tuning condenser and a secondcondenser of relatively low capacity value connected in series acrosssaid coil, and means for short-circuiting said second condenser, saidselecting circuit being so adjusted with respect to said oscillator thatthe signal selected when said second condenser is short-circuitedcombines in said detector with said selected frequency oscillation toproduce a signal at a predetermined intermediate frequency, and that thesignal selected when said smaller condenser is in circuit combines insaid detector with said harmonic frequency oscillation to produce asignal at said same intermediate frequency.

2. A receiver according to claim 1 characterized in that said selectingcircuit is broadly tuned when said second condenser is in circuit and iscomparatively sharply tuned when said second condenser is shortcircuited.

3. A receiver according to claim 1 characterized in that said secondcondenser has a capacity value which is less than the minimum capacityof said variable condenser.

4. A receiver according to claim 1 characterized in that the inductancecoil provides distributed capacity to tune said coil substantially tothe frequency to which it is tuned when said second condenser is notshort-circuited.

5. A receiver according to claim 1 characterized in that when saidsecond condenser is effectively .in circuit, the selecting circuit hasan inductance to capacity ratio which is relatively high, thereby toprovide a broad tuning characteristic.

6. In a radio receiver of the superheterodyne type, the combination witha first detector and an oscillator including means for varying thefrequency thereof, of an inductance coil, a variable condenser and asecond condenser of relatively low capacity connected in seriestherewith, said series condenser combination being connected with saidcoil to provide a tuned circuit preceding said first detector, a switchfor shorting said second condenser, and unitary control means foroperatingsaid frequency varying means and said variable condensersimultaneously,'said coil and said variable condenser having respectiveinductance and capacity values such that when-said switch is closed saidcircuit is tuned to pass a sigdenser having a capacity value such thatwhen said switch is open the radio frequency selecting circuit is tunedwithin a band of frequencies which beat with a harmonic frequency ofsaid oscillator to produce a signal at said intermediate frequency. 1

7. In a superheterodyne receiver, a radio frequency selecting circuittunable within two differing frequency ranges, a tunable oscillatorincluding means for producing fundamental frequency oscillations andharmonic oscillations therof, a detector electrically coupled with saidselecting circuit and said oscillator, said selecting circuit and saidoscillator being simultaneously tunable for selecting signals in one ofsaid frequency ranges, whereby over said one frequency range the signalpassed by the selecting circuit beats with the fundamental frequencyoscillations of said oscillator to produce a signal at a predeterminedintermediate frequency, and means for independently adjusting the tuningofthe,

selecting circuit whereby the selecting circuit is rendered ineffectivefor tuning control over the other frequency range and a signal passedthereby beats with a selected harmonic oscillation of said oscillator toproduce a signal at said same predetermined frequency.

8. A receiver according to claim 7 characterized in that the tuningadjusting means causes the selecting circuit to be substantially fixedlytuned and responsive to signals over a frequency range which is less inwidth than the value of the intermediate frequency.

9. In a radio receiving system, the combination of a tunable oscillatorcircuit having fundamental and harmonic frequencies, a tunable signalreceiving circuit, means common to each circuit providing electricalcoupling therebetween, unitary means for simultaneously varying thetuning of said circuits to provide a predetermined intermediatefrequency signal in response to received signals, and additional tuningmeans in said signal receiving circuit for simultaneously adjusting thetuning of said circuit for broad response within a differingpredetermined signal frequency range wherein signals beat with harmonicfrequency oscillations in the oscillator circuit to provide the saidintermediate frequency signals, and rendering said first named variabletuning means substantially inefiective to vary the tuning of said signalreceiving circuit within the last named frequency range.

10. In a radio receiving system,.the combination of a tunable oscillatorcircuit, a tunable signal receiving circuit, means common to eachcircuit providing electrical coupling therebetween, said last namedmeans being substantially independent of frequency change, unitary meansfor simultaneously varying the tuning .of said circuits to provide apredetermined intermediate frequency signal in response to receivedsignals, said tuning means in the receiving circuit including aninductance, a variable condenser therefor and a second condenser inseries with said variable condenser, said second condenser having acapacity lower than the minimum capacity of said variable condenserwhereby oper\ ation of said variable condenser is ineffective tosubstantially vary the tuning of said receiving circuit, and means forshort circuiting said second condenser to render said variable condensereffective as cuit.

11. In a radio receiving system, a tunable oscillator circuit havingfundamental and harmonic frequencies, a tunable signal receivingcircuit, an electric discharge device having grid electrodes connectedwith each of said circuits and having a common output circuit wherebysaid circuits are electrically coupled with said output circuit,-unitary means for simultaneously varying the tuning of said oscillatorand signal receiving circuits to provide a predetermined frequencysignal in response to received signals, and additional tuning means insaid signal receiving circuit for simultaneously adjusting the tuning ofsaid signal receiving circuit for broad response within a differingpredetermined signal frequency range wherein signals beat with harmonicfrequency oscillations in the oscillator circuit to provide the saidintermediate frequency signals and rendering said first named variabletuning means substantially'ineifective to vary the tuning of said signalreceiving circuit within the last named frequency range.

12. In-a superheterodyne receiver, the combination of a signal receivingcircuit comprising an inductance, a variable tuning condenser thereforand'a second condenser in series with said variable condenser, anoscillator, an electron discharge device providing a common couplingmeans between said oscillator and said receiving circuit, saidoscillator and receiving circuit being simultaneously tunable, saidsecond condenser having a capacity value lower than the minimum capacityof said variable tuning condenser, and means for selectively shortcircuiting said second condenser thereby to tune said receiving circuitwithin a differing signal frequency range, and said second condenser andinductance having respective capacity and inductance values such thatwhen said second condenser is in circuit, the signal receiving circuitis tuned within a frequency range of signals adapted to beat with theoscillator frequency to produce the predetermined intermediate frequencyof the receiver.

; 13. A receiver'according to claim 7 characterized in that the tuningadjusting means causes the selecting circuit to be tuned tosubstantially a fixed frequency within the other frequency rangeindependently of the tuning of the oscillator.

14. A receiver according to claim '7 characterized in that the tuningadjusting means causes the selecting circuit to be broadly tuned tosubstantially a fixed frequency in the middle of the other frequencyrange independently of the tuning of the oscillator.

15. In a superheterodyne receiver, an oscillator, including variabletuning means for producing oscillations having a selected frequency anda harmonic frequency thereof within a predetermined tuning range,variable tuning means for selecting a radio signal within apredetermined tuning range, means for combining said oscillations with aselected signal to produce a signal at a predetermined intermediatefrequency, common means for simultaneously operating said first andsecond named variable tuning means, and means for rendering said secondnamed variable tuning means ineffective to select signals and responsiveto signals in a differing predetermined range effective to beat withsaid harmonic frequency oscillations to produce a signal at said sameintermediate frequency,

a'tuning-means inxsaid receiving cirwhereby the oscillator tuningdetermines the signal selection.

16. In a radio receiving system, the combination with a combineddetector-oscillator electric discharge device, of a signal selectingcircuit, an oscillator circuit, said circuits being connected with saiddevice, uni-control means for tuning said circuits through predeterminedrelated frequency ranges to provide a predetermined beat

